Determine the equilibrium pH of aqueous solutions for the following strong acids

[tobyracine]

Determine the equilibrium pH of aqueous solutions for the following strong acids or bases: (a) 257mg/L of HSO₄^- ; (b) 10nM NaOH ; (c) 75ug/L of HNO₃

 

[AGNuke]

Look for their respective K_a values on net.

 

[tobyracine]

I kind of figured it out except for the first one, because HSO4- can become an acid or a base depending what it's mixed with so I don't know what to do, do I get the pH or the pOH? And how?

 

[Borek]

H₂SO₄ is so strong you can safely ignore HSO₄^- hydrolysis (but you are right mentioning it, compare http://www.chembuddy.com/?left=pH-calculation&right=pH-amphiprotic-salt).

 

[tobyracine]

Thanks

 

[JohnRC]

Not totally relevant to the OP, but part (b) of this exercise is nonsensical in any practical terms. I bring this up because we are in the "Chemistry" forum rather than the "Chemistry Homework" forum.

The answer to a formal calculation to part (b) will only bear any relationship to reality if the concentration of carbon dioxide/bicarbonate in the water is much smaller than that of the hydroxyl -- say 1 nM or less. Any normal aqueous solution will be acting as a carbonate buffer for such low levels of hydroxyl, and I would like to know how anyone proposes to prepare a water sample that is accessible for normal laboratory work, but less than 1 nM in bicarbonate/carbon dioxide.

 

[Borek]

It is a typical trick question asked every year

And heck, you are right about homework... Moving the thread.

toby: please read forum rules.